Vertebrate bone is a composite material comprised of impure hydroxyapatite, collagen, and a variety of noncollagenous proteins, as well as embedded and adherent cells. Vertebrate bone can be processed into an implantable biomaterial, such as an allograft, for example, by removing the cells and leaving behind the extracellular matrix. The properties of the processed bone biomaterial depend upon the specific processes and treatments applied to it and may incorporate characteristics of other biomaterials with which it is combined. For example, bone-derived biomaterials may be processed into load-bearing mineralized grafts that support and integrate with the patient's bone, for example, as described in our commonly owned U.S. Pat. No. 6,123,731, or may alternatively be processed into soft, moldable or flowable demineralized bone biomaterials that have the ability to induce a cellular healing response, for example, as described in our commonly owned U.S. Pat. No. 5,814,476.
The use of bone grafts and bone substitute materials in orthopedic medicine is well known. While bone wounds can regenerate without the formation of scar tissue, fractures and other orthopedic injuries take a long time to heal, during which time the bone is unable to support physiologic loading unaided. Metal pins, screws, rods, plates and meshes are frequently required to replace the mechanical functions of injured bone. However, metal is significantly more stiff than bone. Use of metal implants may result in decreased bone density around the implant site due to stress shielding. Physiologic stresses and corrosion may cause metal implants to fracture. Unlike bone, which can heal small damage cracks through remodeling to prevent more extensive damage and failure, damaged metal implants can only be replaced or removed. The natural cellular healing and remodeling mechanisms of the body coordinate removal of bone and bone grafts by osteoclast cells and formation of bone by osteoblast cells. Ultimately, bone grafts are largely replaced by the recipient's own bone tissues.
The use of bone grafts is limited by the available shape and size of grafts. Bone grafts using cortical bone remodel slowly because of their limited porosity. Traditional bone substitute materials and bone chips are more quickly remodeled but cannot immediately provide mechanical support. In addition, while bone substitute materials and bone chips can be used to fill oddly shaped bone defects, such materials are not as well suited for wrapping or resurfacing bone. Thus, it is desirable to provide a tissue-derived implant that can be used to repair two-dimensional defects and whose remodeling rates are shorter than those of cortical bone.
A variety of implants having application as artificial bone, ligaments, tendons, cartilage, and the like, are also known. U.S. Pat. No. 4,089,071 describes a material for making bone endoprostheses featuring a laminated structure of net-like construction. U.S. Pat. No. 5,092,887 describes an elongated artificial ligament made from demineralized bone which is said to exhibit compliant elasticity and high longitudinal strength. U.S. Pat. No. 5,263,984 describes a prosthetic ligament made up of a quantity of substantially aligned, elongated filaments each of which is a biocompatible, resorbable fibril made, e.g., of collagen, elastin, reticulin, cellulose, algenic acid or chitosan. U.S. Pat. No. 5,711,960 describes an implant, useful inter alia, as a prosthetic or filling for a defective bone, which utilizes, as a base material, a biocompatible bulk structure of a three-dimensionally woven or knitted fabric of organic fibers whose surfaces have been biologically activated or inactivated. U.S. Pat. No. 6,090,998 describes a bone implant, useful for the repair or replacement of ligaments, tendons and joints, which includes at least one mineralized segment and at least one demineralized, flexible segment. Still, it would be useful to provide a one- or two-dimensional implant of interlocking fibrils for use in orthopedic and other tissue engineering applications.